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Lucy's 'great-grandfather' found

Anthropologists say they have discovered the 3.6 million-year-old partial skeleton of a creature that came from the same species as Lucy, but was 400,000 years older and at least as good at walking upright. Their analysis suggests that upright walking, the trademark trait for humans and their extinct kin, goes back further in time than some might have assumed.

This skeleton, described in the Proceedings of the National Academy of Sciences, has a much longer name than Lucy: It was dubbed Kadanuumuu, which means "big man" in Ethiopia's Afar language. Like the 3.3 million-year-old Lucy skeleton, Kadanuumuu was found in the East African country's Afar region, and shares the species name Australopithecus afarensis.

Australopiths are fossil species that share some traits with chimpanzees - for instance, protruding faces and small brains - but share other traits with humans. Most importantly, their skeletons appear to have been built for upright walking. Arizona State University paleoanthropologist Donald Johanson, who discovered Lucy back in 1974, said the latest discovery adds to a "treasure trove" of hundreds of australopith fossils from East Africa.

"It's like the El Dorado of paleoanthropology," he told me.

Piecing together the evidenceThe first bone of Kadanuumuu's skeleton was found in 2005 in the Woranso-Mille area of the Afar region, about 30 miles north of where Lucy was discovered. Over the three years that followed, more than 30 additional bones were unearthed and pieced together for analysis.

CMNH / PNAS

Elements of the partial australopith skeleton known as Kadanuumuu are arranged here anatomically.

The head of the research team, Yohannes Haile-Selassie of the Cleveland Museum of Natural History, told me that Kadanuumuu's skeleton was clearly made for walking, based on measurements of bones including the limbs, clavicle and shoulder blade, the rib cage and the pelvis. In fact, its arrangement was better-suited for upright walking than Lucy's, even though it came from an earlier time in evolutionary history. The key measurement indicated that Kadanuumuu's lower limbs were more elongated than Lucy's - which would make walking easier.

When Lucy was found, scientists thought her species was in the midst of a transition from tree-climbing to upright walking, but Kadanuumuu's larger skeleton suggests that the transition was already made hundreds of thousands of years earlier. (Haile-Selassie and his colleagues assume that Kadanuumuu was male, based on his size as well as the configuration of his pelvis.)

"There is good grounds that advanced humanlike walking actually evolved long before people thought," Haile-Selassie said.

So why did Lucy seem less-suited for upright walking? Haile-Selassie says it's because she was exceptionally small. Over the past 35 years, other specimens of Australopithecus afarensis have been found that suggested a body size larger than Lucy, and even larger than Kadanuumuu. "This individual is among the largest, but not the largest of all the specimens that we've found so far," Haile-Selassie said.

Kadanuumuu is thought to have stood 5 to 5½ feet tall, while Lucy stood only 3½ feet tall. That's not unusual: Anthropologists have found that A. afarensis exhibited significant size differences between the male and the female of the species, a quality known as sexual dimorphism. The diminutive stature of Lucy, which is still the most complete australopith skeleton found to date, may have initially led some scientists down the wrong path, Haile-Selassie said. "Most of the misinterpretations were largely based on the size of Lucy and her sex," he told me.

Findings fit in with ancient footprintsIf the conclusions made by Haile-Selassie and his colleagues are correct, the saga of how we became human is much more ancient than some might have thought. But in fact, the conclusions are consistent with another famous find, the 1976 discovery of the Laetoli footprints in Tanzania. Those prints, which were preserved in volcanic ash 3.6 million years ago, led scientists to suggest that upright walking was mastered well before Lucy's time. "What we have now is the skeletal evidence to complement those footprints," Haile-Selassie said.

Johanson agreed. "This supports much of what we've known before" about the ability of australopiths to walk upright, he told me. He's not fully convinced, however, that Kadanuumuu was significantly better-built for walking than Lucy was. "I'm not quite sure they really have enough to say that the lower limb is elongated," he said.

All this could lead anthropologists to look further back for the origins of upright walking. Perhaps Australopithecus anamensis, which lived in East Africa between 4.2 million and 3.9 million years ago, was the species that picked up the trick. Perhaps it all started with Ardipithecus ramidus, which is thought to have split its time between the trees and the ground in Ethiopia 4.4 million years ago (though there's some controversy over that claim).

That doesn't mean Australopithecus afarensis is out of the spotlight when it comes to studying human origins. Johanson said Lucy and her kin provide an "important reference for assessing other hominid species," in large part because so many specimens have been found over such a wide span of evolutionary time. Going forward, paleoanthropologists may well turn to Lucy, Kadanuumuu and other members of the species to unravel the deeper secrets of ancient human development.

"You can begin to look at the minutiae of microevolution over time," Johanson said, "which is where we're heading."